Several protocols have been designed for transferring messages to selective call receivers. These protocols include POCSAG (Great Britain's Post Office Code Standardization Advisory Group) and GSC (Golay Sequential Code). A message comprises an address if the message is a "tone only" message, or an address and information if the message is a data message. The information in a data message conventionally comprised one of several information formats including numeric (transmitted by BCD), alphanumeric (transmitted by ASCII), or voice (transmitted by digital or analog).
A preamble of a POCSAG signal comprises a number of zero-to-one transitions for bit synchronization. The first word following the preamble is a sync code word which contains a predetermined binary sequence used for frame synchronization. Sixteen words of information, each comprising a selective call address and an associated message, follow before the sync code is repeated. The structure of the addresses and information may be referred to as the signalling format.
In a GSC selective call network, the receivers are divided into a plurality of groups and a twenty three bit code in the preamble selects one of the groups in addition to providing means for bit and frame synchronization. Following the preamble, a start code indicates that the preamble is finished and the information following contains selective call addresses of selective call receivers within the group and messages for those selective call receivers in a pattern of sixteen information words followed by one start code word.
However, in both POCSAG and GSC, as in other known protocols, the information contained within each message comprised only one information format. This may be inefficient, for example, when an alphanumeric (ASCII) message contains mostly numbers. The transmission time could be substantially reduced if the numbers were sent in a numeric (BCD) format.
Thus, what is needed is a selective call receiver that combines two or more received transmissions, each having different information formats, for presentation of the resultant message.